In many of the existing information reproducing apparatuses, reproduction is being made of information recorded on a read-only optical disc such as CDs and CD-ROMs. For example the CD on its surface is recorded, as concave-and-convex formed information, with pits having a size nearly a wavelength of laser light to be used during reproduction and a depth of about one-fourth of that wavelength. The phenomenon of light interference is utilized in reproducing information.
Meanwhile, on the market are rewritable recording mediums adopting a scheme represented by a magneto-optical recording scheme and phase shift recording scheme, realizing high density information recording. For example, in the phase change recording scheme, laser light is illuminated to a recording medium formed on a surface with a phase change film to cause temperature at a laser light illumination spot. By changing the intensity of laser light, binary recording due to crystalline and amorphous forms has been feasible. The information thus recorded is reproduced by illuminating laser light to the recording medium with intensity lower than that of recording and distinguishing between a crystallization phase and an amorphous phase due to the intensity of its reflection.
In reproducing information recorded on the read-only optical disc, a lens optical system is used which has being employed for the conventional optical microscope. Due to limitation by light diffraction, it is impossible to reduce the spot size of laser light less than a half wavelength. Consequently, in the case of further increasing the information recording density of the optical disc, the pit size or track pitch is reduced and hence the information recording unit is reduced to a smaller size than the laser light wavelength. Thus, information reproduction is not feasible.
Meanwhile, in a recording medium recorded with information by the magneto-optical recording scheme and phase change recording scheme, information recording/reproduction with density is realized due to microscopic spot of laser light. Accordingly, the information recording density on the recording medium is limited to the spot size obtainable by focusing laser light. Accordingly, in the conventional optical information recording apparatus adopting a magneto-optical recording scheme and phase change recording scheme, it has been impossible to reduce the spot size obtained by focusing laser light to smaller than a laser light diffraction limit, i.e. a half wavelength of laser light.
On the other hand, there is a proposal of an information reproducing method/apparatus utilizing near-field light created through a microscopic aperture having a diameter smaller than a wavelength of utilized laser light, e.g. approximately 1/10th of the wavelength.
Conventionally, as an apparatus utilizing near-field light there has been a near-field microscope employing a microscopic aperture as above, being utilized for observing a microscopic surface structure of a sample. As one of near-field light utilizing schemes for the near-field microscope, there is a scheme (illumination mode) that the distance between a probe microscopic aperture and a sample surface is brought close to nearly a diameter of the probe microscopic aperture so that propagation light is introduced through the probe and directed to the probe microscopic aperture, thereby creating near-field light in the microscopic aperture. In this case, the created near-field light and the sample surface interact with to cause scattering light to be detected by a scattering light detecting system, accompanied by an intensity or phase reflecting a sample surface fine structure. Thus, observation is possible with high resolution not realizable by the conventional optical microscope.
Meanwhile, as another scheme of a near-field microscope utilizing near-field light, there is a scheme (collection mode) that propagation light is illuminated to a sample to localize near-field light on a sample surface whereby the probe microscopic aperture is brought close to the sample surface nearly to an extent of a diameter of the probe microscopic aperture. In this case, the localized near-field light and the probe microscopic aperture interact to cause scattering light to be introduced to a scattering light detecting system through the probe microscopic aperture, accompanied by an intensity or phase reflecting a sample surface fine structure. Thus, high resolution observation is realized.
The information reproducing method/apparatus utilizing near-field light as mentioned above utilizes these observation schemes for the near-field microscope.
Accordingly, the utilization of near-field light makes possible information reproduction (reading) from the information recording medium recorded exceeding the recording density on the conventional information recording medium.
In the meanwhile, in order to realize reproduction of information recorded on the recording medium through utilizing near-field light mentioned above, there is a necessity for probe proximity control technology to bring a probe microscopic aperture portion as an optical head and a surface of the recording medium to a fully-close distance of from several nano-meters to 10 nano-meters.
In the conventional hard disc technologies, there is a flying head technology to bring a recording head and a recording medium close to each other. The float amount of the flying head from a recording medium surface is about from 50 nano-meters to 100 nano-meters, which value is too great to realize information reproduction utilizing near-field light.
On the other hand, the scanning probe microscopes (SPM) represented by the scanning tunnel microscope (STM) or atomic force microscope (AFM) are used in order to observe nano-meter order microscopic regions on sample surfaces. The SPM uses a tip sharpened probe to detect a physical amount, such as a tunneling current or inter-atomic force caused between the probe and the sample surface, whereby scanning is made on the sample surface in proximity to the sample surface to obtain high resolution image.
Accordingly, this SPM probe proximity technology is applicable to a near-field microscope or a recording apparatus utilizing near-field light. Thus, the recording medium and the probe microscopic aperture at its tip can be kept in a fully closed state.
In this case, however, there arises a need to detect by respective unique mechanisms a physical amount replaced by information recorded on the recording medium, or near-field light, and a physical amount required to effect proximity control of the probe, or inter-atomic force, making complicated the overall apparatus structure.
Also, because the SPM probe proximity technology requires a sharpened tip for the probe, it is not necessarily an optimal method for the near-field microscopes using a flat-surface probe without having a sharpened tip or the recording apparatuses utilizing near-field light.
Meanwhile, near-field light mentioned above abruptly attenuates in a z direction provided that a line connecting between the probe and the recording medium is defined as a z direction. Accordingly, the probe if deviates in position in the z direction from the recording medium surface due to a certain cause, this induces a variation in the output signal. The presence or absence of a data mark on the recording medium increases and decreases the output signal. Thus, there has been a problem that, when there is a change in the output signal, it cannot be reliably determined whether the change is due to the presence of the data mark or due to deviation in probe position in the z direction.
There is a method for controlling the probe z-direction position by mechanically vibrating the probe in the z direction to keep the amplitude constant. However, this result in giving a physical impact to the recording medium surface, incurring damage to the recording medium and probe. Meanwhile, there has been difficulty in reducing apparatus size due to probe vibration control and amplitude detecting mechanism.
Therefore, it is an object of the present invention to provide in view of the above-stated problems a recording apparatus to realize, with a simple structure, reproducing and recording information reliably for a recording medium having high density record.